1. Field of the Invention
The invention relates to a method of manufacturing a composite wafer structure, and more particularly, to a method of manufacturing a composite wafer structure which actively controls fracture induced during the manufacture of the composite wafer structure and further protects the composite wafer from undesired edge damage.
2. Description of the Prior Art
Composite wafer structure, such as a Silicon-on-insulator (SOI) structure, has been applied extensively to be the substrate of a semiconductor process or a microelectromechanical process. Below is an example of a typical SOI structure to illustrate the edge damage which often occurs during the manufacture of a composite wafer structure.
Please refer to FIG. 1; FIG. 1 is a sectional view of a typical SOI structure 1. The SOI structure 1 basically includes a device wafer 12 and a base wafer 14.
As shown in FIG. 1, the device wafer 12 has a bond surface 122 and a bottom surface 124. According to the process of manufacturing the SOI structure 1, the device wafer 12 is bonded to the top surface 142 of the base wafer 14 with its own bond surface 122. In particular, a silicon oxide layer 16 is formed on the bond surface 122 of the device wafer 12 and/or the top surface 142 of the base wafer 14 before the bonding process. FIG. 1 is an example of the oxidized layer 16 only formed on the top surface 142 of the base wafer 14. In addition, an annealing treatment can be performed to the bonded device wafer 12 and the base wafer 14 to enhance the bonding strength between the device wafer 12 and the base wafer 14. Generally, a chemical mechanical polishing (CMP) process will be performed on the bottom surface 124 of the device wafer 12 until the initial thickness of the device wafer 12 is reduced to an expected thickness.
However, because of the limitation on the alignment of the processing machines itself, after the bonding of the device wafer 12 and the base wafer 14, the top surface 142 of the base wafer 14 and the bond surface 122 of the device wafer 12 cannot tightly bond together at the edges thereof, and a gap remains between the edges thereof. During the subsequent grinding process to the bottom surface 124 of the device wafer 12 to reduce the thickness of the device wafer 12, the edge of the device wafer 12 described above cannot bear the load from the grinding machines, and further unexpected fracture will occur, which is called edge damage (as No. 126 shown in FIG. 1). The edge damage of the SOI structure described above will lower the available area of the SOI structure and will waste material of the wafer in the consequent process of manufacturing semiconductor integrated circuit; it will even reduce the yield rate of the mass production regarding the SOI structure. Notice that the problem of edge damage described above also happens easily in other types of composite wafer structures.
A lot of literature with regard to reducing the probability of edge damage of SOI structure during the manufacturing process have been disclosed and are listed as follows: U.S. Pat. Nos. 5,823,325; 6,541,356 and 6,717,217.
Through understanding of prior arts, they obviously are all based on the view of passive fracture control to prevent the occurrence of fracture. However, mass production regarding the composite wafer structure by applying the prior arts cannot prevent the edge damage. Furthermore, the complexity of the manufacturing process is also increased in some prior arts.
Comparing with the prior art, the manufacture of the composite wafer structure enclosed in the present invention is based on the view of active fracture control. It is to say, fracture (different from the fracture which can cause edge damage) will certainly happen and should be controlled, so as to enhance the process of manufacturing composite wafer structure.